1. Field of the Invention
The invention is concerned with a device for the separation of blood and, more specifically the invention is concerned with a device for the separation of blood with a cannula using a single needle, with recirculation.
2. Description of Related Technology
A blood separation device of the type mentioned above is known, for example, from DE-OS 39 31 471 (published Apr. 11, 1991) or the Journal of Clinical Apheresis, Volume 6, pages 24-27 (1991), the respective disclosures of which are incorporated by reference herein.
In comparison to the continuous two-needle method, the single-needle method provides the advantage that the donor has to be punctured with a cannula only once. This is especially advantageous when the puncturing conditions are poor.
On the other hand, in the single-needle method, two cycles must be performed. In a collection cycle, blood is drawn from a vein and introduced into a centrifuge for separation, where the blood fractions to be collected and recycled are separated. In a return cycle, the fractions to be returned to the donor are transported back, for example, with the aid of a second pump, as described in the DE-OS 39 31 471 or with the aid of a device that exerts pressure on a storage bag.
Two problems arise in the single-needle method, namely intolerance to the anticoagulant added to the blood, which depends on the patient, and the partially limited effectiveness of the separation.
Firstly, blood donors exhibit different tolerance to anticoagulant, which is mostly added in the form of ACD-A, upon return to the vein of the arm. At high blood return flow rates, large amounts of anticoagulant are returned to the donor. On the other hand, at low return rates, the time required for return is lengthened correspondingly. Therefore, it is desirable to have the possibility of adjusting the return flow rate.
As mentioned in DE-OS 39 31 471, the partially limited effectiveness of the separation can be improved by recirculation of the return blood. However, DE-OS 39 31 471 does not disclose what control means are used in the case of the blood pump used therein being used as a return pump and in the case of the second pump that is included in the return circuit thereof.